Clinical Assessment And Quantitative Methods

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Previously, dermatological studies of the skin have scored the degree of urticaria by means of visual assessment by an experienced observer, usually a dermatologist. There are several advantages and disadvantages to this technique. Advantages are that it is inexpensive, visual scoring is rapid, subjects are regularly assessed so that the study can be curtailed if adverse reactions are severe, and unexpected findings can be handled by the investigator. However, simple observation may introduce error, inter- and intraobserver variation. This is especially important in larger studies, which may involve a team of investigators.

Visual observations are also often graded on an ordinal (nonlinear) scale (e.g., rating reactions as weak, moderate, or severe). As these data are not in linear numerical form, that statistical analysis is not as powerful as for quantitative data. In many studies, subjects report symptoms, also on an ordinal scale; this, again, is a subjective analysis prone to variation error.

In contrast, a quantitative analysis may provide linear numerical data that are easily reproducible and accurate in standardized conditions. Rather than providing a score, measured data allow for statistical comparison such as mean values and standard deviations. This adds to our understanding of the properties of the test substance. Thus, objective measurements can clearly benefit dermatology studies.

Table 2 Scale to Score Erythema

Score Description

1 + Slight erythema, either spotty or diffuse.

2 + Moderate uniform erythema. 3+ Intense redness.

4+ Fiery redness with edema.

Source: Ref. 18a.

Visual Scoring of Contact Urticaria

Contact urticaria can be graded visually by marking the degree of erythema and edema on an ordinal scale. Tables 2 and 3 provide examples.

Measurement of Erythema

Erythema, redness of the skin, is part of the skin inflammatory response that reflects localized increase in capillary blood flow elicited. Therefore, erythema can be measured by both the redness and the blood flow in the inflamed area.

Measuring Color

Two techniques have been used to measure color: remittance spectroscopy and tristimulus chromametry. Elsner gave detailed descriptions of the two techniques (19,20). Essentially, both methods detect light remitted from illuminated skin. Remittance spectroscopy employs multiple sensors to ''scan'' the light over the whole visible spectrum, producing a spectrogram. This differs from a tristimulus chromameter, in which the remitted light is transmitted to three photodiodes, each with a color filter with a specific spectral sensitivity: 450 nm (blue),

Table 3 Scale to Score Edema



Slight edema, barely visible or palpable. Unmistakable wheal, easily palpable. Solid, tense wheal. Tense wheal, extending beyond test

Source: Ref. 18b.

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